The present invention relates to compositions and methods for lanthionizing keratin fibers using a combination of at least one multivalent metal hydroxide and at least one complexing agent effective for dissociating the at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of the keratin fibers. In one embodiment, the process of lanthionizing keratin fibers results in relaxed or straightened hair.
In today""s market, there is an increasing demand for the hair care products referred to as hair relaxers, which relax or straighten naturally curly or kinky hair. A hair relaxer can be a product that is applied in a hair salon by a professional or in the home by the individual consumer. One of the benefits of straightening or relaxing the curls of very curly hair is an increase in hair manageability and ease of styling.
Normally, the hair relaxing process is a chemical process which alters the chemical bonds in the hair and forms lanthionine. Hair fiber, a keratinous material, contains proteins or polypeptides many of which are bonded together by disulfide bonds (xe2x80x94Sxe2x80x94Sxe2x80x94). A disulfide bond that is formed from the sulfhydryl groups (xe2x80x94SH) of two cysteine residues results in a cystine residue. While there are other types of bonds which occur between the polypeptides that make up hair, such as salt bonds, the permanent curling or the shape of the hair is essentially dependent on the disulfide bonds of cystine residues.
As a result, relaxing or straightening of hair can be achieved by disrupting the disulfide bonds of the hair fibers with an alkaline or a reducing agent. The chemical disruption of disulfide bonds by an alkaline agent is usually combined with mechanical straightening of the hair, such as combing, where straightening occurs through changing of the relative positions of opposite polypeptide chains. The reaction is subsequently terminated by rinsing and/or the application of a neutralizing composition.
The alkaline reaction is normally initiated by hydroxide ions. Not to be limited by theory, there are two reaction sequences that are predominantly used to explain the disruption of the disulfide bonds in hair by hydroxide ions, both of which result in lanthionine formation. One sequence is a bimolecular nucleophilic substitution mechanism where the hydroxide ion directly attacks the disulfide linkage, resulting in the formation of lanthionine and HOS. See Zviak, C., The Science of Hair Care, 185-186 (1986). The second is a xcex2-elimination reaction initiated by the attack of a hydroxide ion on a hydrogen atom located on the carbon atom that is in the xcex2-position to the disulfide bond. Id. The result is the formation of dehydroalanine, which in turn reacts with the thiol of the cysteine or the amine group of the alanine to form lanthionine and lysinoalanine. Regardless of the mechanism, the release of hydroxide ions that can penetrate the hair drives the hair relaxing process through a cystine to lanthionine transformation. Thus, the term lanthionizing is used when one skilled in the art refers to the relaxing or straightening of keratin fibers by hydroxide ions.
Most frequently, relaxing compositions are in the form of gels or emulsions that contain varying proportions of strong bases that are water soluble, such as sodium hydroxide, or compositions that contain slightly soluble metal hydroxides, e.g., calcium hydroxide (Ca(OH)2), that are converted in situ to soluble bases, e.g., guanidine hydroxide. Traditionally, the two main technologies used in the hair care industry for generating hydroxide to relax keratin fibers are referred to as xe2x80x9clye,xe2x80x9d or sodium hydroxide, relaxers or xe2x80x9cno lyexe2x80x9d relaxers. The xe2x80x9clyexe2x80x9d relaxers use sodium hydroxide in a concentration range of generally 1.5 to 2.5% (0.38-0.63 M) depending on the base or carrier used, the condition of the hair, and the speed of relaxation desired. Sodium hydroxide is extremely effective in straightening the hair but can result in a reduction in hair strength and, in some cases, partial or total loss of hair through breakage. Some manufacturers market lithium and potassium hydroxide relaxers as xe2x80x9cno lyexe2x80x9d but, while this is technically true, these relaxers still rely on the soluble hydroxides of the inorganic potassium or lithium.
Most other xe2x80x9cno lyexe2x80x9d relaxers operate by obtaining hydroxide from a slightly soluble source such as Ca(OH)2. For example, the slightly soluble Ca(OH)2 is mixed with guanidine carbonate to form the soluble but unstable source of hydroxide, guanidine hydroxide, and the insoluble calcium carbonate (CaCO3). The reaction is driven to completion by the precipitation of CaCO3 and is in effect substituting one insoluble calcium salt for another. Because guanidine hydroxide is fundamentally unstable, the components are separated until the time of use.
Guanidine carbonate and calcium hydroxide, however, create a different set of problems. The insoluble byproduct, CaCO3, leaves a white residue or unattractive xe2x80x9cwhiteningxe2x80x9d or xe2x80x9cashingxe2x80x9d that remains in the hair since divalent metals like calcium have a relatively good affinity to keratin. A decalcifying shampoo is subsequently needed to remove the ashing.
Thus, there is still a need for a process to relax keratin fibers that has the advantages of using an insoluble metal hydroxide, such as Ca(OH)2, but reduces or eliminates the problem of ashing caused by the insoluble byproduct, CaCO3.
To achieve these and other advantages, and in accordance with the purpose of the invention as embodied and broadly described herein, the present invention, in one aspect, provides a composition for lanthionizing keratin fibers comprising at least one multivalent metal hydroxide and at least one complexing agent effective for dissociating said at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of said keratin fibers. The at least one complexing agent may be chosen from, but is not limited to, organic acids and salts thereof and, in a preferred embodiment, is chosen from amino- and hydroxy-carboxylic acids, amino- and hydroxy- sulfonic acids, and amino- and hydroxy-phosphonic acids. However, the at least one complexing agent may not be only guanidine tartrate or only guanidine phosphate or only a mixture of guanidine tartrate and guanidine phosphate. The at least one multivalent metal hydroxide may be chosen from, but is not limited to, calcium hydroxide, barium hydroxide, magnesium hydroxide, aluminum hydroxide, cupric hydroxide, strontium hydroxide, molybdenum hydroxide, manganese hydroxide, zinc hydroxide, and cobalt hydroxide.
The present invention is also drawn to a method for lanthionizing keratin fibers to achieve relaxation of the keratin fibers by generating hydroxide ions in an ionizing solvent by adding to at least one multivalent metal hydroxide an activating composition wherein the activating composition comprises a complexing agent or a mixture of complexing agents effective for dissociating the at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of the keratin fibers; forming a composition containing the generated hydroxide ions; and applying the composition to keratin fibers for a period of time to lanthionize the keratin fibers. The lanthionization is terminated when the desired level of relaxation of the keratin fibers has been reached. The reverse process may also be used, i.e. the addition of the multivalent metal hydroxide to a composition comprising a complexing agent that is effective for dissociating at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of the keratin fibers.
Complexing agents for use in the methods of the invention may be chosen from, but are not limited to, organic acids and salts thereof and in a preferred embodiment are chosen from amino- and hydroxy-carboxylic acids, amino- and hydroxy-sulfonic acids, and amino- and hydroxy-phosphonic acids. However, the complexing agent(s) may not be only guanidine tartrate or only guanidine phosphate or only a mixture of guanidine tartrate and guanidine phosphate.
Multivalent metal hydroxides for use in the methods of the invention may be chosen from, but are not limited to, calcium hydroxide, barium hydroxide, magnesium hydroxide, aluminum hydroxide, cupric hydroxide, strontium hydroxide, molybdenum hydroxide, manganese hydroxide, zinc hydroxide, and cobalt hydroxide.
The invention also provides for a multicomponent kit for lanthionizing keratin fibers, wherein the kit comprises at least two separate components. One component of the kit contains a composition for generating hydroxide ions that comprises at least one multivalent metal hydroxide while the other component of the kit contains an activating composition comprising a complexing agent or mixture of complexing agents that are effective for dissociating the at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of the keratin fibers.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Reference will now be made in detail to the presently preferred embodiments of the present invention. The invention, in one aspect, provides a composition for lanthionizing keratin fibers comprising at least one multivalent metal hydroxide and at least one complexing agent effective for dissociating the at least one multivalent metal hydroxide in a sufficient quantity to effect lanthionization of keratin fibers, wherein the at least one complexing agent may not be only guanidine tartrate or only guanidine phosphate or only a mixture of guanidine tartrate and guanidine phosphate.
Not to be limited as to theory, the lanthionization of keratin fibers is driven by the release of hydroxide ions, which disrupt the disulfide bonds of cystine. The compositions of the present invention offer advantages over traditional xe2x80x9clyexe2x80x9d or xe2x80x9cno-lyexe2x80x9d hair relaxers by providing a novel way of generating soluble hydroxide ions from metal hydroxides while still being effective to relax or straighten the hair.
As described above, the hair relaxing compositions of the prior art utilized soluble metal hydroxides or slightly soluble metal hydroxides. Slightly soluble metal hydroxides, including most divalent metal hydroxides, are not soluble enough in water to generate sufficient soluble hydroxide ions to effect lanthionization of keratin fibers. This can be represented by the following, in which the equilibrium favors the left side of the reaction:
M(OH)2(solid)⇄M++(aq.)+2OHxe2x88x92(aq.).
Therefore, in traditional relaxers containing slightly soluble metal hydroxides, the equilibrium was pushed to the right side and the reactions driven to completion by the precipitation of M++ as an insoluble compound such as CaCO3.
The compositions of the present invention, however, utilize a complexing agent to dissociate the multivalent metal hydroxide and chelate or sequester the M++. The complexing agent and the multivalent metal form a complex that in most cases has a stronger interaction between the complexing agent and the metal. As a result, the complexing agent removes the metal from the above reaction medium and allows the equilibrium to be shifted to the right side.
The complexing agent may be a chelating agent or sequestering agent that leads to a partial or full dissociation of the multivalent metal hydroxide. Regardless, the complexing agent chelates, sequesters or otherwise ties up the counter ion of the hydroxide, allowing more hydroxide ions to be liberated into solution. In other words, the net effect of the complexation is the generation of enough soluble hydroxide ions to effect lanthionization of keratin fibers without relying on the precipitation of M++ as an insoluble compound such as CaCO3.
The complexing agents of the present invention include, but are not limited to, any chelating agents or sequestering agents. A chelating agent is a compound or ligand that can bind to a metal ion, usually through more than one ligand atom, to form a chelate. See Lewis, R. J., Hawley""s Condensed Chemical Dictionary p. 240 (1997). A chelate is usually a type of coordination compound in which a central metal ion such as Co2+, Ni2+, Cu2+, Ca2+ or Zn2+ is attached by coordinate links to two or more nonmetal atoms, i.e., ligands, in the same molecule. Common chelating agents include ethylene-diaminetetraacetic acid (EDTA), nitrilotriacetic acid, and ethylenegylcol-bis(xcex2-amino-ethyl ether)-N,N-tetraacetic acid.
Sequestering agents may be any material that prevents an ion from exhibiting its usual properties due to close combination with that material. Id. at 991. Certain phosphates, for example, form a coordination complex with metallic ions in solution so that the usual precipitation reactions are prevented and calcium soap precipitates are not produced from hard water treated with certain phosphates and metaphosphates. Id. Other examples of sequestering agents include hydroxy carboxylic acids such as gluconic, citric and tartaric acids. Id.
Examples of complexing agents that may be useful in the practice of the invention include, but are not limited to, organic acids and salts thereof. The salts of the organic acids of the present invention may contain an organic or inorganic cation. In a preferred embodiment, the complexing agent is chosen from mono-, di-, or poly-, amino- and hydroxy-carboxylic acids, mono-, di-, or poly-, amino- and hydroxy-sulfonic acids, and mono-, di-, or poly-, amino- and hydroxy-phosphonic acids.
In a further preferred embodiment, the complexing agent is chosen from ethylene diamine tetraacetic acid (EDTA) and its salts; N-(hydroxyethyl) ethylene diamine triacetic acid and its salts; aminotrimethylene phosphonic acid and its salts; diethylenetriamine-pentaacetatic acid and its salts; lauroyl ethylene diamine triacetic acid and its salts; nitrilotriacetic acid and its salts; iminodisuccinic acid and its salts; tartaric acid and its salts; citric acid and its salts; and N-2-hydroxyethyliminodiacetic acid and its salts. The salts may be chosen from salts with organic or inorganic cations. In one embodiment, the inorganic cation is chosen from potassium, sodium or lithium.
The complexing agent may also be chosen from a phosphate or silicate that demonstrates chelating or sequestering properties such as tripotassium or trisodium phosphate, or disodium or dipotassium silicate; an amino acid; or a crown ether. In one embodiment, an amino acid such as monosodium glutamate, which is a known calcium chelator, is used as a complexing agent.
Depending on the nature of the complexing agent, the solubility in the reaction medium of the complex formed between the complexing agent and the metal ion may vary. In a preferred embodiment, the complexing agent-metal ion complex is considered by one of ordinary skill in the art to be soluble in the reaction medium. In another embodiment, a composition of the invention provides for a complexing agent-metal ion complex that has a solubility in water of greater than 0.03% at 25xc2x0 C. and a pH of 7.0, and preferably greater than 1% at 25xc2x0 C. and a pH of 7.0.
In a further preferred embodiment, a salt of EDTA, such as sodium, lithium, potassium or guanidine EDTA, is the complexing agent. EDTA has a strong calcium binding constant over a wide range of pH. For example, tetrasodium EDTA solubilizes calcium hydroxide in aqueous media to give a clear solution. The use of a complexing agent, such as tetrasodium EDTA, that solubilizes the metal ion of a multivalent metal hydroxide offers the benefits of no xe2x80x9cashingxe2x80x9d. However, the use of complexing agents that do not completely solubilize the metal ion and only form slightly soluble or sparingly soluble complexing agent-metal ion complexes is also within the practice of the invention.
In another embodiment, the complexing agent may be a xe2x80x9csoftxe2x80x9d base or cation, e.g., organic cations such as guanidine, mono-, di- or tri-ethanolamine, and other amines, and a chelating or sequestering anion. A combination of a xe2x80x9csoftxe2x80x9d base or cation and a chelating or sequestering anion may be effective if the xe2x80x9csoftxe2x80x9d cation exists at a high enough pH to achieve straightening. For example, amino acids such as arginine may be used to neutralize EDTA to make a xe2x80x9csoft basexe2x80x9d/strong chelator pair. However, while many guanidine xe2x80x9csoftxe2x80x9d cation complexing agents such as guanidine EDTA are within the practice of the invention, the use of only guanidine tartrate or only guanidine phosphate or only a mixture of guanidine tartrate or guanidine phosphate, which have been listed in at least one reference as salts that may be used in place of guanidine carbonate to drive the of production of OH through precipitation (see, e.g., U.S. Pat. No. 5,565,216 to Cowsar and Adair), are not within the practice of the invention. Guanidine tartrate or guanidine phosphate may be used within the practice of the invention, however, as part of a mixture comprising one or more complexing agents as defined herein.
The present invention also provides for a simple screening test to determine the applicability of a complexing agent for use in the lanthionizing compositions of the present invention. By titrating a suspension of a multivalent metal hydroxide, such as Ca(OH)2, with the complexing agent of interest, the chelating or sequestering properties may be observed. If the solution reaches a pH sufficient for lanthionizing keratin fibers, then the complexing agent is a good candidate for use in the compositions of the present invention.
In a further preferred embodiment, the complexing agents of the present invention offer one or more of the following benefits: compatibility with keratin conditioning ingredients (polyquats, polymers, proteins, alkylquaternary ammonia compounds, silicones, etc); a stable mixture of complexing agent and multivalent metal hydroxide that can be stored for later use, an advantage which is not possible with compositions that result in the unstable guanidinium hydroxide; and the absence of a precipitation by-product and/or the absence of the need to apply a decalcifying shampoo after relaxing.
Mixtures of complexing agents including mixtures of at least one chelating agent and at least one sequestering agent are also within the practice of the invention. In one embodiment, a less active chelating agent such as pentasodium aminotrimethylene phosphonate, may be mixed with a more active chelating agent, such as EDTA, to achieve the desired lanthionization of keratin fibers at a slower rate.
The multivalent metal hydroxides useful in the present invention may be any multivalent metal hydroxide that is effective for providing hydroxide ions to lanthionize keratin fibers when mixed with a complexing agent. In a preferred embodiment, the multivalent metal hydroxide is chosen from any alkali insoluble or slightly soluble hydroxide including but not limited to, calcium hydroxide, barium hydroxide, magnesium hydroxide, aluminum hydroxide, cupric hydroxide, strontium hydroxide, molybdenum hydroxide, manganese hydroxide, zinc hydroxide and cobalt hydroxide.
The compositions of the present invention may be provided as a one part composition comprising the multivalent metal hydroxide and the complexing agent or in the form of a multicomponent kit. The multicomponent kit for lanthionizing keratin fibers comprises at least two separate components. A first component of the kit contains a composition for generating hydroxide ions that comprises at least one multivalent metal hydroxide. This first component may be in the form of an emulsion, solution, suspension, gel or paste. A second component of the kit contains an activating composition comprising a complexing agent or mixture of complexing agents that are effective for dissociating the at least one multivalent metal hydroxide in sufficient quantity to effect lanthionization of keratin fibers. This second component may also be in the form of an emulsion, suspension, solution, gel or paste. The skilled artisan, based on the stability of the composition and the application envisaged, will be able to determine how the composition and/or multicomponent compositions should be stored and mixed.
In a preferred embodiment, one of the components of a multicomponent kit will contain enough water or other ionizing solvent to ensure that, upon mixing, enough of the generated hydroxide ions remain in solution to effect lanthionization of keratin fibers.
The compositions of the present invention may also include ion exchange resins such as silicates. In one embodiment the silicate is a zeolite and more preferably a zeolite clay. The ion exchange resins may increase relaxing efficiency or enable the skilled artisan to control the rate of generation of soluble hydroxides. In a multicomponent kit, the ion exchange resin may be formulated with the insoluble metal hydroxide component or with the complexing agent component or may be a third component that is added to one or both of the metal hydroxide and complexing agent components.
Not to be limited as to theory, it is believed that the ion exchange resin participates in the lanthionizing process through an ion exchange mechanism. The ion exchange reversible reaction, which is the interchange of the multivalent metal ions from the multivalent metal hydroxide to the ion exchange resin, releases hydroxide at a much slower rate than does the complexing agent. Thus, the ion exchange resin can be used in combination with a complexing agent to modulate or control the rate of release of the soluble hydroxide, producing a mixed composition for more gentle or partial relaxing.
Any ion exchange resin which is effective in participating in the lanthionizing process is within the practice of the invention, including, but not limited to, silicates of aluminum and an alkali metal such as sodium, lithium, potassium or combinations thereof including analcime, chabazite, gmelinite, harmotome, levynite, mordenite, epistilbite, heulandite, natrolite, stilbite, edingtonite, mesolite, scolecite, thomosonite, brewsterite, faujasite, gismondine, laumontite, phillipsite, and aluminosilicate.
The present invention is also drawn to a method for lanthionizing keratin fibers to achieve relaxation of the keratin fibers. The methods of the present invention comprise generating hydroxide ions in an ionizing solvent by adding an activating composition to at least one multivalent metal hydroxide. The activating composition comprises a complexing agent or a mixture of complexing agents effective for dissociating the multivalent metal hydroxide in sufficient quantity to effect lanthionization of the keratin fibers. A composition containing the generated hydroxide ions is formed and the composition is applied to keratin fibers for a period of time to lanthionize the keratin fibers. The lanthionization is terminated when the desired level of relaxation of the keratin fibers has been reached.
The ionizing solvent is preferably a solvent that lowers the ionic bonding forces in the solute molecules enough to cause separation of their constituent atoms. In a further preferred embodiment the ionizing solvent is chosen from water and dimethyl sulfoxide (DMSO).
The method also encompasses forming the hydroxide ions in situ, i.e., while on the keratin fibers, by mixing at least multivalent metal hydroxide and at least one activating composition in the presence of the keratin fibers.